A spot where light is collected by an objective lens always needs to be positioned in the focusing direction and the tracking direction, and therefore, control bands for focusing and tracking need to be increased in accord with improvement in the rotation speed of an optical disc. Additionally, in order to realize stable control, higher order resonance frequencies of an objective lens actuator need to be approximately five times or greater than the control bands. Since the higher order resonance of the objective lens actuator is due to the elastic resonance of a lens holder, in order to increase the high order resonance frequencies, the stiffness of the lens holder needs to be increased.
In such optical disc drive, the objective lens actuator is an apparatus for driving an objective lens that collects light on a recording surface of an optical disc in the focusing direction (the direction in which the objective lens is moved closer to/farther from the optical disc surface) and in the tracking direction (radially with respect to the optical disc).
As a method for realizing such objective lens actuator with higher stiffness, Patent Document 1 is directed to improving stiffness, based on improvement in the higher order resonance frequencies of the lens holder, by changing the elastic constant of the material of the lens holder that holds the objective lens.
[Patent Document 1] JP Patent Publication (Kokai) No. 2006-209875 A (FIG. 52)